Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Chemistry and Biochemistry

First Advisor

Cheng Zhang


Increasing energy demand, petroleum prices, global warming, and depleting fossil fuel resources are the main challenges faced by the human beings. Many scientists are searching for sustainable and alternative sources of fossil fuels as solutions to these challenges. Lignocellulosic biomass is one of the renewable and eco-friendly abundant sources that has been considered by both academia and industry sectors as a renewable source for bio-oil and chemicals. Direct liquefaction of biomass in the sub-/super-critical solvent has considered a practical method to convert lignocellulosic material into liquid fuel. However, undesirable properties such as poor stability, low energy value, and high acidity and heteroatoms content are the main drawbacks of bio-oil generated by the liquefaction method. Elimination of these undesirable properties is necessary before the bio-oil can be utilized for co-processing in refineries alongside petroleum crude oil or used as transportation and engine fuels directly. To improve the biomass liquefaction process, the research presented in this dissertation focuses on the chemistry of direct biomass liquefaction in terms of product distribution and yields of liquefaction, the influence of liquefaction parameters, and role of catalysts. In chapter 2, pine sawdust liquefaction was catalyzed by different concentrations of NaOH, metals, and metallic salts in H2O, EtOH, and a mixture of EtOH and H2O. The liquefaction results showed that liquefaction in H2O at 200°C gave low bio-oil yields. While in the co-solvent liquefaction, higher yields of bio-oil were obtained at 240°C and 260°C in comparison with that achieved at 200°C. In solvolytic liquefaction (only EtOH used as solvent), pine sawdust was effectively liquefied, and higher production of bio-oil was generated by metals with high reduction power. Based on the results revealed in this chapter, outcomes of pine sawdust liquefaction are highly determined by solvent and temperature more than other parameters. In chapter 3, many investigations were conducted to determine the influence of residence time, biomass: base ratio, metal oxide, and Ni metals for the development of a catalytic system for corn stover liquefaction. The results suggested that high bio-oil yields could be obtained using Ni metal combined with Fe2O3 under the basic condition at (8:1) ratio of biomass/base. In chapter 4, liquefaction of different biomass such as corn stover, birch, switchgrass, pine sawdust, and sugarcane bagasse using various catalytic systems were investigated. The synergistic effect of Ni metal-metal oxide in the presence of NaOH showed a more significant influence on biomass liquefaction, depending on the type of biomass and metal oxide used. The results are consistent with what was presented in chapter 3. Bio-oil production was more promoted under basic than neutral conditions. Lower percentages of protons attributed to aromatic and oxygenated species were measured in bio-oils generated under basic conditions compared to those measured under neutral conditions. The distribution of bio-oil components is highly determined by the type of biomass and catalysts used. In chapter 5, to achieve better improvements in the quality and cost-effectiveness of bio-oils generated from direct liquefaction, Fe, Zn, and Ni metals were used in combination with a salt for liquefaction of corn stover under different conditions. KOAc was found to be a more effective base than NaOH. High bio-oils ( >40%) and low SR (< 6%) yields with low oxygen content were achieved from corn stover liquefaction at 300°C for < 4 hr using Ni metal-Fe2O3- KOAc and Zn metal, Ni(OAc)2, KOAc.

Library of Congress Subject Headings

Lignocellulose -- Biotechnology.
Biomass energy.
Liquid fuels.
Renewable energy sources.



Number of Pages



South Dakota State University


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Available for download on Tuesday, December 20, 2022

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